A few extra kilos aren’t so good for you after all

It’s a myth that people who weigh a bit more than average live longest. A recent analysis of 30 million people shows that those who had a normal weight had the lowest risk of premature death.

BMI:Healthy non-smokers are at the lowest risk of premature death if they have a BMI between 20 and 24. It is a myth that a few extra kilos are good for you.

Sorry, it’s best for your health if your weight is normal. Illustration: Thinkstock

A research report showing that people with a body mass index (BMI), which corresponds to being overweight (BMI 25-30) live longer than people with a normal weight (BMI 18.5-25) was a sensation in both Norwegian and international media a few years ago. The study also showed that people with a BMI that means they are moderately obese (30-35) were at no higher risk of early death than people with a normal body weight, and that this risk only increases for people who are extremely obese (with a BMI greater than 35).

Weeding out sources of error

A research team consisting mainly of researchers from NTNU in Trondheim has taken a second look at the matter, picking out the weaknesses that the previous analysis had. The analysis involved over 30 million people, and they’ve come to a quite different result.

If everyone who has smoked at some point in their life is removed from the analysis, the risk of early death is suddenly lowest at a BMI of 23-24.

When the researchers removed everyone who had a chronic illnesses at the time that the BMI data was collected, they found the lowest risk of premature death was at a BMI of 22-23. And when they only included studies with a long follow-up, only healthy non-smokers with a BMI between 20 and 22 don’t have to worry about dying prematurely as a result of their extra kilos.

Smokers and people with chronic illness have a low BMI

On average, smokers and chronically ill people have a lower BMI. This can cause misleading statistics if you don’t take it into consideration. Photo: Thinkstock

“Smokers are at a much higher risk of chronic illness and premature death due to over 20 different diseases, but also generally have a lower BMI than non-smokers. Because of this correlation between smoking and both low weight and premature death, we have to exclude smokers from studies like this to get accurate results,” says Dagfinn Aune, who was the head author of an article recently published as the lead article in the prestigious British Medical Journal.

Chronic illness can also cause sudden weight loss. In addition, people who are chronically ill are at a much higher risk of premature death. The results from studies that were over a shorter period of time are generally more affected by chronically ill people who have lost weight, but have no diagnosis.

What is BMI?

Body Mass Index (BMI) is a way to measure the relationship between height and weight, and is used as an international indicator of obesity. You can calculate your BMI using the relation (weight[kg])/(height[m])². You can also use this online BMI calculator.

Note: The limits for what determines a child's healthy weight are different than for adults and are dependent on age.

Source: CERG

“Both smoking and chronic disease can therefore contribute to the overestimation of what optimal BMI is, because these conditions superpose with benefits on the low end of the BMI scale. This is difficult to adjust for statistically. The previous meta-analysis hadn’t done this well enough, but this time we’ve done a better job,” Aune explains.

30 million participants

Aune and his research colleagues included 230 studies that looked at the relationship between BMI and death due to varying causes. All told, these studies has over 30 000 000 participants, where 3 700 000 died during the follow-up of the study. This is more than ten times as many participants and deaths as the previous meta-analysis, which only included studies where the participants were categorised only by their BMI.

The studies examined by the researchers involved more than 30 million people. Illustration: Thinkstock

“Another shortcoming of the previous analysis is that many of the larger studies used more refined BMI-categories to define the relationship between BMI and mortality better. These studies had therefore been excluded. In addition, there has been a number of new studies about this since the previous analysis was published,” says Aune.

The previous analysis showed that a BMI of 25 meant lowest risk of death, while both higher and lower BMIs lead to increasing risk of mortality.

People who are overweight according to the BMI-scale are at no higher risk of premature death than someone with a normal BMI of 23, but anyone with a BMI indicating obesity is at a significantly higher risk.

The analysis of non-smokers comprised of 10 000 000 participants and 740 000 deaths, and showed that both overweight and obesity leaded to a significant risk of premature death.

In the analysis of healthy non-smokers in studies with a long follow-up period, a person with a BMI of 20 was at no higher risk of premature death than a BMI of 23, but those with a BMI at the higher end of the normal range, as well as people who are overweight and obese are all at a higher risk of premature death.

Over half of Norwegian adults are overweight, and one in five has a BMI that means they are obese. Being overweight and obese are linked to a number of conditions, including cardiovascular disease and a number of forms of cancer.

BMI is not perfect, but it is a useful indication. Photo: Thinkstock

“Our finds show that a BMI that corresponds to being overweight or obese can mean an increased risk of premature death. But the BMI scale doesn’t differentiate between muscle mass and fat, so it isn’t a perfect indicator of whether a person is overweight or obese. However, in most cases, there is a significant correlation between BMI and body fat percentage,” Aune says.

He points out that a person’s BMI is a worse indicator of body fat percentage as that person gets older, because the amount of illness and weight loss due to illness increase with age. In addition, we lose muscle mass as we age, so a low BMI for an older person may just mean low muscle mass. Adding waist measurement and a waist-hip ratio can help give a better idea of fat distribution.

No, this question isn’t only for people who’ve smoked a lot. Seven factors, including two new ones, can predict whether you have a high risk of developing lung cancer.

MORE NORWEGIAN SCITECH NEWS

LOADING CONTENT

Privacy Policy

The Privacy Statement is about how this website collects and uses visitor information. The statement contains information that you are entitled to when collecting information from our website, and general information about how we treat personal data.The legal owner of the website is the processing officer for the processing of personal data. It is voluntary for those who visit the web sites to provide personal information regarding services such as receiving newsletters and using the sharing and tip services. The treatment basis is the consent of the individual, unless otherwise specified.

1. Web analytics and cookies (cookies)

As an important part of the effort to create a user-friendly website, we look at the user pattern of those who visit the site. To analyze the information, we use the Google Analytics analysis tool.Google Analytics uses cookies (small text files that the site stores on the user's computer), which registers the users' IP address and provides information about the individual user's online movements. Examples of what the statistics give us answers to are; how many people visit different pages, how long the visit lasts, what websites users come from and what browsers are used. None of the cookies allow us to link information about your use of the site to you as an individual.The information collected by Google Analytics is stored on Google servers in the U.S.. The information received is subject to the Google Privacy Policy.An IP address is defined as a personal information because it can be traced back to a particular hardware and thus to an individual. We use Google Analytics's tracking code to anonymize the IP address before the information is stored and processed by Google. Thus, the stored IP address can not be used to identify the individual user.

2. Search

If the webpage has search function, it stores information about what keywords users use in Google Analytics. The purpose of the storage is to improve our information service. The search usage pattern is stored in aggregate form. Only the keyword is saved and they can not be linked to other information about the users, such as the IP addresses.

3. Share / Tips service

The "Share with others" feature can be used to forward links to the site by email, or to share the content of social networking. Tips for tips are not logged with us, but only used to add the tips to the community. However, we can not guarantee that the online community does not log this information. All such services should therefore be used wisely. If you use the email feature, we only use the provided email addresses to resend the message without any form of storage.

4. Newsletter

The website can send out newsletters by email if you have registered to receive this. In order for us to be able to send e-mail, you must register an e-mail address. Mailchimp is the data processor for the newsletter. The e-mail address is stored in a separate database, not shared with others and deleted when you unsubscribe. The e-mail address will also be deleted if we receive feedback that it is not active.

5. Registration, form

The website may have a form for registration, contact form or other form. These forms are available to the public to perform the tasks they are supposed to do.Registration form is for visitors to sign up or register.Contact form is for visitors to easily send a message to the website's contact person.We ask for the name of the sender and contact information for this. Personal information we receive is not used for purposes other than responding to the inquiry.The form is sent as email via Mailgun as a third party solution. The entire submission will be stored at Mailgun for 24 hours. Between 24 hours and 30 days, only mailheader is stored before the submission is deleted after 30 days. The reason for this storage is to confirm whether emails are sent from the website and forwarded to the correct recipient.Once the email is received by the recipient, it is up to the recipient to determine the data processing needs of the email.

6. Page and service functionality

Cookies are used in the operation and presentation of data from websites. Such cookies may contain language code information for languages ​​selected by the user. There may be cookies with information supporting the load balancing of the system, ensuring all users the best possible experience. For services that require login or search, cookies can be used to ensure that the service presents data to the right recipient.